• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.521-524
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• 2005

To protect a satellite and electronic equipment from the acoustic loads generated by rocket propulsion system, many launch vehicle use acoustic blanket. Most high frequency region of the acoustic loads is reduced by nose fairing skins and acoustic barrier, but low frequency region is not. In order to control low frequency acoustic mode, we designed away resonator panel which was made of composite materials. This paper shows the absorption coefficient measurement result of resonator and SPL(Sound Pressure Level) reduction by using resonators in a rectangular cavity for experiment. Proper arrangement of acoustic resonators at each mode reduce effectively SPL around the satellite through changing boundary condition.

• Water for future
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• v.28 no.6
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• pp.133-146
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• 1995

Manning's roughness coefficient for the Han River (from Paldang dam to Indo Bridge) is estimated by one-dimensional unsteady flow model, NETWORK. The entire river is divided into two regions, one region of Paldang dam to Kwangjang, and another region of Jamsu Bridge to Indo Bridge, and changes of the roughness coefficient according to changes in discharge are estimated using data of the past flood events. Estimated roughness coefficients are compared with previous results. Finally, the stage variation according to the variation of channel roughness is presented.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.2
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• pp.78-84
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• 2001

The daily streamflow in the Yaluhe watershed located in the north-eastern part of China was simulated by DAWAST model and the water balance parameters of the model were calibrated by simplex method. Model verification tests were carried out. The range of root mean square error was 0.34∼1.50mm, that of percent error in volume was -16.9∼-62.0% and that of correlation coefficient was 0.727∼0.920. DAWAST model was revised to consider the phreatic evaporation from the ground water in the frozen soil by adjusting soil moisture content in the unsaturated layer at the end of the melting season. The results of estimation of the daily streamflow by the revised model were statistically improved, that is, the range of root mean square error was 0.31∼1.49mm, that of percent error in volume was -11.7∼-12.1%, and that of correlation coefficient was 0.810∼0.932. The accuracy of DAWAST model was improved and the applicability of DAWAST model was expanded to the frozen region.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.228-233
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• 2000

The Korean Next Generation Reactor(KNGR) is a Pressurized Water Reactor adopting direct vessel injection(DVI) to optimize the performance of emergency core cooling system(ECCS). In a certain accident, however, pressurized thermal shock(PTS) of the vessel due to the sudden contact with the injected cold water is expected. In this paper, an accident of Main Steam Line Break(MSLB) has been numerically investigated with direct vessel injections and an increased volume flow rate in some cold legs. Using FLUENT code, temperature distributions of the fluid in the downcomer and of reactor vessel including the core region have been calculated, together with the distribution of convective heat transfer coefficient(CHTC) at the cladding surface of the reactor vessel. The result shows that some parts of the core region of the reactor vessel have higher temperature gradient expressing higher thermal stress.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.1
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• pp.42-50
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• 1991

The purpose of this study is an augmentation of heat transfer in the case of upward rectangular impinging water jet system. The variables of this study are nozzle-to-heated surface distance, jet velocity and supplementary water height. Optimum heights of supplementary water which augment the heat transfer rate are S/B=2 for H/B=30 and S/B=I for H/B=40, 50. On the Y-direction of nozzle, there exhibits the secondary peak of heat transfer coefficient when supplementary water is not used, however using the supplementary water, it does not exhibits. In the case of using supplementary water, heat transfer coefficient increases not only in stagnation region but also in wall jet region.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1258-1266
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• 2004

It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer. In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to dimensionless parameters such as Sherwood number, Stanton number and Colburn j-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more suitable for turbulent boundary layer. But average Sherwood number and average Colburn j-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar boundary layer as well as turbulent boundary layer.

• The Journal of Fisheries Business Administration
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• v.52 no.3
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• pp.1-14
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• 2021

The proportions of both the fishery industry and the gross regional domestic product in the national economy are gradually decreasing. If high value-added processed fishery products suitable for regional characteristics are developed, these proportions can be improved. In pursuit of this, it is first necessary to discover processed fishery products specialized in each region and then establish a development framework for them. In this study, location coefficient was used to find processed fishery products specialized in each region. Then, dynamic shift-share analysis was used to establish a development framework which consisted of four development types of processed fishery products. Based on the magnitudes of the industrial mix effect and the regional shift effect, the supporting strategy directions were proposed for four development types of processed fishery products. The supporting strategy directions were all focused on revitalizing the local economy.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.5
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• pp.19-24
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• 2004

Entrainment of ambient gas into a transient diesel spray is a crucial factor affecting the following preparation of combustible mixture. In this study, the entrainment characteristics of ambient gas for a non-evaporating transient diesel were investigated using a common-rail injection system. The effects of ambient gas density and nozzle hole geometry were assessed with entrainment coefficient. Laser Doppler Velocimetry (LDV) technique was introduced to measure the entrainment speed of ambient gas into a spray. There appeared a region where the entrainment coefficients remained almost constant while injection rates were still changing. The effect of common-rail pressure, which altered the slope of injection rate curve, was hardly noticed at this region. Entrainment coefficient increased with ambient gas density, that is, the effect of ambient gas density was greater than that of turbulent jet whose entrainment coefficient remained constant. The non-dimensional distance was defined to reflect the effect of nozzle hole diameter and ambient gas density together. The mean value of entrainment coefficient was found to increase with non-dimensional distance from the nozzle tip, which would be suggested as the guideline for the nozzle design.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.649-654
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• 2019

Stable haptic interaction with virtual environments is essential not only for the safety of the user but also for improving the immersion of the user. If the coefficient of a virtual spring is increased, the system becomes unstable. Therefore, the coefficient of the virtual spring is limited. The haptic system with the high-frequency zero-order-hold (HF-ZOH) is proposed to enhance the stability margin of a virtual spring. In this paper, the relationship among the sampling period of HF-ZOH, the coefficient of the physical damper, and the maximum stable margin of the virtual spring is analyzed. The lager the coefficient of the physical damper is, the shorter the sampling period of the HF-ZOH is, the larger the stable region of the virtual spring becomes. If the ratio N is larger than 40, the stable region of the proposed method is about three times to eight times that of the previous method, according to the coefficient of the physical damper. Hence the method enables to improve the user's realism in virtual environments.

• Atmosphere
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• v.26 no.1
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• pp.127-140
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• 2016

In this study, the correlations between AST850 and precipitation, and those between WDT and precipitation in the Yeongdong coastal region under the direct/indirect influence of the expansion of cP (continental polar air mass) high were quantitatively analyzed based on the winter season data for the last 20 years, according to surface pressure patterns such as Type 1 (cP high expansion type), Type 2 (cP high expansion + trough type), Type 4 (South trough type), and Type 5 (East Sea trough type). Here, AST850 represents 'sea surface temperature minus temperature on 850 hPa level' and WDT represents 'a speed of 1000 hPa wind projected onto a certain wind direction times precipitation duration in hour'. First, the correlation coefficients between AST850 and precipitation in Type 1, Type 2, and Type 5 cases were 0.253, 0.384, and 0.398 respectively, indicating that a tendency of increasing precipitation linearly with the value of AST850 is slightly presented. In the case of Type 4, however, the coefficient was -0.15, representing almost no linear correlation between AST850 and precipitation. In the correlation between WDT and precipitation, there was the largest correlation coefficient (0.464) between WDT along a direction of $90^{\circ}$ and at EN1 in Type 1 cases. In the case of Type 2, there was the largest correlation coefficient (0.767) between WDT along a direction of $67.5^{\circ}$ and at ES1. In the case of Type 4, there was the largest correlation coefficient (0.559) between WDT along a direction of $22.5^{\circ}$ and at EN2. Finally, in the case of Type 5, there was the largest correlation coefficient (0.945) between WDT along a direction of $315^{\circ}$ and at SE1, representing the largest coefficient among the types. It was found that surface wind directions with the highest correlations to precipitation in the Yeongdong coastal area on winter season were varied according to surface pressure patterns, and that the correlations between WDT and precipitation were higher than those between AST850 and precipitation.